1. Field of the Invention
This invention relates to a system for removing exhaust particles produced by an engine, such as a diesel engine.
2. Description of the Prior Art
The exhaust from diesel engines contains pollutive particles. A filter is conventionally used to remove pollutive particles from the engine exhaust. As the filter traps the particles, it clogs. A known way of rejuvenating a clogged filter is to increase the temperature of the engine exhaust above a certain level and thereby to burn off the particles from the filter.
Particular additive agents pre-mixed with engine fuel can lower the minimal exhaust temperature necessary for rejuvenating a clogged filter, since the additive agents included in the engine exhaust facilitate burning of the particles deposited on the filter.
Japanese patent publication No. 59-201916 discloses exhaust cleaning systems for diesel engines. These systems include an upstream filter and a downstream filter disposed in an engine exhaust passage. The upstream filter is designed to trap pollutive exhaust particles. When the upstream filter clogs, a burner is activated to increase the exhaust temperature to burn off the particles from the filter. An additive agent included in engine fuel lowers the minimal exhaust temperature necessary for rejuvenating the upstream filter. The additive agent generates pollutive ashes. The downstream filter is designed to trap these ashes. As the downstream filter traps the ashes, it clogs.
Accordingly, it is necessary to periodically replace the downstream filter.